Refactor theme change handler for safe async updates

Refactored OnThemeChanged in MainLayout.razor to use InvokeAsync for proper synchronization of UI updates and async logic, preventing threading issues. Also added a blank line after app.Run() in Program.cs (no functional impact).

DbFirst.BlazorWebApp/Program.cs

@@ -44,4 +44,4 @@ app.UseAntiforgery();
 app.MapRazorComponents<App>()
     .AddInteractiveServerRenderMode();
 
-app.Run();
+app.Run();